1. Field of the Invention
The present invention relates to an image reading apparatus, and, more specifically, to the one which is preferred for use in a document reading device such as an image reader, a facsimile machine, a digital copying machine, or the like.
2. Related Background Art
An image reading apparatus is known in which both an image sensor module and a heat source are housed in the same unit with the image sensor module disposed in the vicinity of the heat source; for example, an image sensor module is stacked on top of a laser-beam printer working as a heat source. In some apparatuses which have such a construction, a partition module is employed to separate the image sensor module from the laser-beam printer as a heat source. In some of these apparatuses, a heat insulating material is used in the partition module so that no heat transfer takes place from the laser-beam printer to the image sensor module.
In the conventional apparatuses mentioned above, however, even if the heat insulating material is employed in the partition module, the partition module gradually rises in temperature and reaches its thermal saturation if the apparatus is continuously run for a long time; heat is likely to transfer to the image sensor module, thereby causing its temperature to rise. In the event of temperature rise in the image sensor module, image sensor elements or an illumination device suffer from variations in their performance, deterioration of image sensing reliability and thus picture quality, and in an extreme case, destruction of components which are susceptible to heat. This problem is getting even more serious today, because of the increased frequency of use of apparatuses, the compact design of apparatuses, the increased amount of heat generated due to high-speed capability design, worsening heat radiation environments, and the like.